1. Field of the Invention
This invention relates to an energy beam irradiating apparatus that forms an irradiation pattern on a disc substrate through irradiation with an energy beam.
2. Description of the Related Art
When manufacturing an optical recording substrate (optical disc), such as a CD or DVD, or a magnetic recording substrate for a hard disk apparatus, a stamper in whose surface fine pits and lands are formed is sometimes used. When manufacturing such a stamper, as one example irradiation with an energy beam is carried out using an energy beam irradiating apparatus such as the electron beam irradiation apparatus disclosed in Japanese Laid-Open Patent Publication No. 2001-242300 to form a latent image on a resist layer formed on a surface of a substrate (as one example a disc-like substrate), and fine pits and lands are formed in the resist layer by developing the resist layer. Next, after a metal layer has been formed, by nickel plating for example, on a surface of the substrate in which the fine pits and lands have been formed, the metal layer is peeled off, thereby manufacturing a stamper in whose surface fine pits and lands that are the inverse of the fine pits and lands on the substrate have been formed.
In the energy beam irradiation apparatus in the above-mentioned application, a construction where a body to be irradiated with energy beams is attached by a suction means is used as the support part for supporting the body to be irradiated with energy beams, though the body to be irradiated can be supported by other constructions using means that do not attach the body using suction. For example, as shown in FIG. 13, a construction where a substrate 12 as a body to be irradiated with energy beams is attached to a substrate holder 51 and held between a holder main part 52 and a cover 53 of the substrate holder 51 is also in common use. In this case, as shown in FIG. 14, the holder main part 52 is formed as a square flat plate, for example, and positioning pins 21a, 21a for arranging and positioning the substrate 12 are erected on the upper surface thereof. Also, female-threaded holes 21b, 21b into which conductive fastening bolts 23, 23, . . . (see FIG. 13) are screwed are respectively formed in the four corners of the holder main part 52. On the other hand, as shown in FIG. 15, the cover 53 is formed in the same shape as the holder main part 52 and a circular hole 53a with a smaller diameter than the substrate 12 is formed in a central part thereof. Insertion holes 22c, 22c into which end parts of the respective positioning pins 21a, 21a of the holder main part 52 are inserted are also formed in a surface of the cover 53 that faces the holder main part 52. In addition, insertion holes 22e, 22e, . . . through which the fastening bolts 23, 23, . . . pass are respectively formed in the four corners of the cover 53.
When the substrate 12 is attached to the substrate holder 51, as shown in FIG. 13, first the substrate 12 is attached to the holder main part 52. At this time, as shown by the broken line in FIG. 14, the outer edge of the substrate 12 contacts the respective positioning pins 21a, 21a so that the substrate 12 is positioned at a predetermined mounting position. By doing so, the center of the substrate 12 is aligned with a center of the mounting position. Next, the ends of the respective positioning pins 21a, 21a are inserted into the respective insertion holes 22c, 22c so that the cover 53 covers the holder main part 52. By doing so, relative displacements between the holder main part 52 and the cover 53 are prevented. Next, the fastening bolts 23, 23, . . . pass through the insertion holes 22e, 22e, . . . of the cover 53 and the ends of the fastening bolts 23, 23, . . . are screwed into the female-threaded holes 21b, 21b . . . At this time, since the circular hole 53a of the cover 53 is formed with a smaller diameter than the substrate 12, an outer edge on the upper surface of the substrate 12 contacts the rim of the circular hole 53a on the lower surface of the cover 53 around an entire circumference of the rim. In this way, the substrate 12 is attached to the substrate holder 51 so as to be held between the holder main part 52 and the cover 53.
Next, the substrate holder 51 to which the substrate 12 has been attached is fixed at a predetermined position on a moving stage (composed of a rotating table or an X-Y table) of an energy beam irradiating apparatus. In this case, the substrate holder 51 is correctly fixed at the predetermined position on the moving stage and a center of the mounting position of the substrate holder 51 is aligned with a reference point in a coordinate system (such as an X-Y coordinate system) set in advance on the moving stage. After this, the energy beam irradiating apparatus causes the moving stage to move according to a predetermined movement pattern while carrying out irradiation with an energy beam. In this case, the movement pattern is regulated with the above-mentioned reference point that is set on the moving stage as a reference. For example, the movement pattern is regulated using relative coordinate data in the above-mentioned X-Y coordinate system with the reference point as a reference. This means that when the substrate 12 has been correctly attached to the mounting position of the substrate holder 51 and the substrate holder 51 has been correctly attached to the predetermined position on the moving stage, an irradiation pattern (latent image) corresponding to the movement pattern set with the reference point set on the moving stage as a reference is correctly formed on the resist layer formed on the surface of the substrate 12 by irradiation with the energy beam with the center of the substrate 12 as a reference.
However, by investigating an energy beam irradiating apparatus with the above substrate holder 51, the inventors of the present invention discovered the following problem. That is, since the above energy beam irradiating apparatus is constructed so that the substrate 12 is positioned by two positioning pins 21a, 21a, when the holder main part 52 is covered with the cover 53, there is the possibility of the substrate 12 becoming displaced in a direction moving away from the respective positioning pins 21a, 21a. In this case, the displacement of the center of the substrate 12 with respect to the center of the mounting position results in the center of the substrate 12 becoming displaced with respect to the reference position of the moving stage. Accordingly, there is the problem that it becomes difficult for the energy beam irradiating apparatus to correctly form the irradiation pattern on the substrate 12 with the center of the substrate 12 as a reference. Also, even when the substrate 12 has been correctly attached to the mounting position of the substrate holder 51, there are cases where the substrate holder 51 is fixed at a position displaced from the predetermined position on the moving stage. This means that in such cases also, the center of the substrate 12 is displaced with respect to the reference position on the moving stage, so that it is difficult to correctly form the irradiation pattern on the substrate 12 with the center of the substrate 12 as a reference.
On the other hand, when a stamper for a discrete track medium is manufactured, for example, it is necessary to form a predetermined irradiation pattern (latent image) in the form of a plurality of concentric circles on the resist layer formed on the surface of the substrate 12 with the center of the substrate 12 as a reference and an eccentricity with respect to the center of the substrate 12 of ±10 μm or less. However, the respective displacements that are actually produced when the above substrate 12 is mounted on the substrate holder 51 and when the substrate holder 51 is fixed on the moving stage can result in a displacement of up to around 300 μm between the center of the substrate 12 and the reference point of the moving stage. In this case, the center of an irradiation pattern formed on the resist pattern of the substrate 12 will be displaced by around 300 μm from the center of the substrate 12, so that improvements are desired. Also, when a discrete track medium manufactured using a stamper produced under the above conditions is loaded in a recording/reproduction apparatus, there is also the problem that the time during which a magnetic head can follow a track becomes short.